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Unformatted text preview: HKIN 190 Anatomy & Physiology I Muscle Structure and Physiology II Tissue types in the body – CMEN C onnective Tissue Blood Bone Cartilage Connective Tissue Proper M uscle Smooth Skeletal Cardiac E pithelial Squamous Cuboidal Columnar Pseudostratified Transitional N ervous Learning Objectives 1. To understand the difference between a single “muscle twitch” and a whole muscle contraction. 2. To understand the factors influencing muscle tension. 3. To understand the different types of skeletal muscle fibres/cells. Type I Type IIa Type Iix 4. To understand the difference between isometric, concentric and eccentric muscle contractions. 5. To understand common muscle injuries. 6. To understand the concept of levers in the body. muscle fascicle muscle fibers (cells) myofibrils thick & thin filaments (myosin & actin) sarcomere myofibril muscle fiber fascicle sarcomere Review from last class: 1. How many sarcomeres do you see in this picture? 2. 3. 4. 5. 6. Review: Self Quiz What shortens when the muscle contracts? Learning Objective 1 To understand the difference between a single “muscle twitch” and a whole muscle contraction. We have already discussed the structure of muscle and how a single muscle fibre contracts (excitation-contraction resulting in the shortening of sarcomeres down the length of a single muscle fibre). This is a single l muscle twitch z (one nerve action potential resulting in one muscle fiber contraction) and can be demonstrated in a lab. In reality, many muscle fibres contract simultaneously to produce a whole muscle contraction. Single muscle twitch vs whole muscle contraction single nerve impulse excitation-contraction coupling leading to Latent : AP over sarcolemma, Ca++ released Contraction : Ca++ binds to troponin, cross- bridges form, powerstroke occurs Relaxation : Ca++ actively pumped back into SR, myosin heads detach from actin. Single muscle twitch 2 msec 10-100 msec 10-100 msec Muscle twitch: 20-200 ms Nerve AP: 1 ms Single muscle twitch: 3 phases • latent period – begins with stimulation – AP from motor neuron – during this time, the depolarization is spreading from the motor end plate across the sarcolemma and the T-tubules, release of calcium – this is the period of excitation-contraction coupling • contraction period – tension is rising – this is the time when calcium is binding to troponin and cross-bridges are forming – maximum tension is when the maximum number of cross-bridges have formed • relaxation period – the calcium levels are falling (pumped back into SR), the thin filaments return to resting period where the actin are covered by the tropomyosin – the number of cross-bridges are decreasing Single muscle twitch a single stimulus-contraction-relaxation sequence in a muscle fiber 1 nerve impulse (AP) 1 muscle twitch vary in duration, from 7 up to 200 ms (depending on type of muscle) twitches are too short to contribute to functional activity Single muscle twitch...
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